In response to flaws exposed by an embarrassing nuclear weapons error last August, the Air Force will change the way bomber crews organize for their nuclear training mission, the top Air Force general said Thursday.

Gen. Michael Moseley, the Air Force chief of staff, told reporters that B-52 crews assigned to training for the nuclear attack mission will do that exclusively for at least six months at a time, rather than switching regularly between training for nuclear and non-nuclear missions.

He said the exclusively nuclear training might be as long as 12 months. That detail has not yet been decided.

The idea is to improve B-52 crews' focus on the stringent safeguards built into the nuclear mission, thereby avoiding a repeat of the startling missteps of last August when a B-52 was mistakenly armed with six nuclear-tipped cruise missiles and flown from Minot Air Force Base, N.D., to Barksdale Air Force Base, La. At the time, the pilot and crew were unaware they had nuclear arms aboard.

The error was considered so grave that President Bush was quickly informed.

The Air Force has already taken numerous other steps to improve the nuclear training operations. Moseley said those were in response to recommendations by two panels that closely examined the August incident, which top Air Force leaders said afterward was an "unacceptable mistake."

When the results of the Air Force's own investigation were announced last October, Maj. Gen. Richard Newton, the Air Force deputy chief of staff for operations, attributed the episode to an "unprecedented string of procedural errors" beginning with a failure by airmen to conduct a required inspection of the missiles before they were loaded aboard the B-52 bomber that flew from Minot.